1. Field of the Invention
Aspects of the present invention relate to a membrane electrode assembly (MEA), and more particularly, to a monopolar type MEA having sensing elements that can continuously measure internal state conditions such as temperature or fuel concentration in the MEA.
2. Description of the Related Art
A fuel cell is an electricity generator that converts chemical energy of a fuel into electrical energy through a chemical reaction. The fuel cell can continuously generate electricity as long as the fuel is supplied. Accordingly, when air that includes oxygen is supplied to a cathode electrode and a fuel containing hydrogen is supplied to an anode electrode, electricity is generated by an inverse reaction of water electrolysis through an electrolyte membrane interposed between the cathode and anode electrodes of the fuel cell. A structure in which the cathode electrode, the anode electrode, and the electrolyte membrane are assembled is called a membrane electrode assembly (MEA).
There are various types of fuel cells. Direct methanol fuel cells (DMFCs), which have recently been highlighted, use methanol as the fuel, and has several advantages. Some of the advantages of the DMFC include having high energy density and high current density, not requiring peripheral facilities such as a fuel processor since the methanol is directly fed to the fuel cells, and having ease of storage and supply of the fuel.
Among the DMFCs, a monopolar type DMFC has a structure in which a plurality of unit cells are connected in series, and are arranged on one electrolyte membrane. Thus, the thickness and volume of the monopolar type DMFC can be greatly reduced, and a slim and small DMFC can be manufactured accordingly.
However, monopolar type MEAs that have been used or proposed have a structure that can actively sustain an electricity generation reaction but do not have an element that can directly measure internal state conditions of the fuel cell, such as a temperature change or a fuel concentration change. Accordingly, determination of an optimum condition of a fuel supply or a temperature setting is difficult, and detection of an abnormal operation state of the fuel cell is delayed that may result in damage to the fuel cell.
Accordingly, there is a need to develop a new type of an MEA that is able to detect changes of internal state conditions in the MEA.